Flame Retardant 4 Research Articles

FR4-Based Electromagnetic Scanning Micromirror Integrated with Angle Sensor.

This paper presents a flame retardant 4 (FR4)-based electromagnetic scanning micromirror, which aims to overcome the limitations of conventional microelectromechanical systems (MEMS) micromirrors for the large-aperture and low-frequency scanning applications. This micromirror is fabricated through a commercial printed circuit board (PCB) technology at a low cost and with a short process cycle, before an aluminum-coated silicon mirror plate with a large aperture is bonded on the FR4 platform to provide a high surface quality. In particular, an electromagnetic angle sensor is integrated to monitor the motion of the micromirror in real time. A prototype has been assembled and tested. The results show that the micromirror can reach the optical scan angle of 11.2° with a low driving voltage of only 425 mV at resonance (361.8 Hz). At the same time, the signal of the integrated angle sensor also shows good signal-to-noise ratio, linearity and sensitivity. Finally, the reliability of the FR4 based micro-mirror has been tested. The prototype successfully passes both shock and vibration tests. Furthermore, the results of the long-term mechanical cycling test (50 million cycles) suggest that the maximum variations of resonant frequency and scan angle are less than 0.3% and 6%, respectively. Therefore, this simple and robust micromirror has great potential in being useful in a number of optical microsystems, especially when large-aperture or low-frequency is required.

Sintering process of inkjet-printed silver patterns using a heated inert gas

In this study, we introduce a thermal sintering process using a heated inert gas as a new sintering method. The heated gas flow is formed by passing nitrogen (N2) gas through a heating head of 300 to 700°C, and the desired substrates are then exposed to the heated gas flow through a 400mm long and 5mm wide slit-nozzle. Sintering performance of Ag films was characterized by analyzing the electrical resistivity and metallographic structures according to the temperature change of the heating head. The temperature distribution of the heating region is analyzed by infrared (IR) thermal imaging and surface temperature measured by thermo-label tape. To test the feasibility of the proposed method for application to printed circuit board (PCB) manufacturing, we performed a reliability evaluation using the printed Ag patterns under the standard of the Institute for Interconnecting and Packaging Electronic Circuit (IPC), TM650. Various reliability test patterns were created by Ag inkjet-printing on both a rigid flame retardant 4 (FR4) substrate and a flexible polyimide (PI) film substrate. The reliability evaluation includes withstanding voltage, adhesive strength, thermal shock, pressure cooker, and bending tests. The surface wettability of the substrates was controlled to obtain high quality fine and uniform patterns by UV/O3 treatment after coating a fluoropolymer thin film.

Effects of Solder Volume and Reflow Conditions on Self-Alignment Accuracy for Fan-Out Package Applications

The effects of solder volume and reaction time between molten solder and a metal pad at the peak temperature of reflow on the self-alignment effect have been investigated in flip chip bonding. A glass die with two different pad designs and a flame retardant-4 (FR-4) organic substrate were used. Sn-3.0Ag-0.5Cu and Sn-3.5Ag solders were formed on Cu-organic solderability preservation (Cu-OSP) and electroless nickel electroless palladium immersion gold (ENEPIG) pads on FR-4 substrates using the stencil printing method. To assess the effect of solder volume, the thickness and opening size of the stencil mask were controlled. Reflow experiments were performed at 250°C with wetting times of 40 s, 55 s, 65 s, and 75 s. After flip chip reflow soldering, the bonding areas were cross-sectioned to inspect the shape of the interconnected solder using scanning electron microscopy. The results revealed that using an insufficient solder volume on the pad was responsible for die shifts larger than 1 μm, while a sufficient solder volume on the pad and a stable solder joint shape could ensure misalignment less than 1 μm. The Sn-3.0Ag-0.5Cu solder showed a lower die shift value than the Sn-3.5Ag solder because the Sn-3.0Ag-0.5Cu solder has stronger surface tension than the Sn-3.5Ag solder. Using a longer wetting time between the solder and the pad at the peak temperature also improved the die shift value because the increased reaction time changed the interconnected solder shape between the die and substrate from concave to convex, moving the die to a more accurate position. Furthermore, the restoring forces on die self-alignment influenced the die shift value. A stronger solder surface tension and a larger volume of solder on the pad produced stronger restoring forces for die self-alignment, thereby improving the die shift value.

The determination of the thickness of the layers deposited on the electronic circuit boards through tribological methods

The purpose of the paper is to determinate the thickness of the copper layer deposit on the electronic circuit boards, the thickness of the soldering alloy SAC 307 (96.5%Sn/3.0%Ag/0.7%Cu) deposit on the copper-PCB assembly used in electronic industry and also to determinate the sliding length of the sphere on those materials. Slurry composed of water and SiC was used to reduce the testing time. For the experiment a CSEM Calowear equipment was used and the tested materials were the layer of FR4(flame retardant 4) with copper deposit and the soldering alloy SAC 307.

A Novel Metamaterial Enhanced Microwave Testing System for Bare PCB Substrates Using Image Rendering Approach

This paper proposes a method for detection of cracks in bare printed circuit board sheets before etching of interconnects and mounting dies. A microwave planar sensor probe is designed, and the impedance matching property is used for anomaly detection in flame retardant-4 sheets. The proposed technique and apparatus is first validated through finite-integration-based technique and then through measurement. The resonant frequency information thus obtained is then plotted on a 2-D gradient representation matrix. A novel Windows VB-based application software is developed to determine the dimensions of the crack in the sample through various interpolation operations and dimensioning technique on the image matrix. These are then effectively displayed in a graphical user interface.

Effects of Aging Treatment on Mechanical Properties of Sn-58Bi Epoxy Solder on ENEPIG-Surface-Finished PCB

The mechanical properties of Sn-58Bi epoxy solder were evaluated by low-speed shear testing as functions of aging time and temperature. To determine the effects of epoxy, the interfacial reaction and mechanical properties of both Sn-58Bi and Sn-58Bi epoxy solder were investigated after aging treatment. The chemical composition and growth kinetics of the intermetallic compound (IMC) formed at the interface between Sn-58Bi solder and electroless nickel electroless palladium immersion gold (ENEPIG) surface finish were analyzed. Sn-58Bi solder paste was applied by stencil-printing on flame retardant-4 substrate, then reflowed. Reflowed samples were aged at 85°C, 95°C, 105°C, and 115°C for up to 1000 h. (Ni,Pd)3Sn4 IMC formed between Sn-58Bi solder and ENEPIG surface finish after reflow. Ni3Sn4 and Ni3P IMCs formed at the interface between (Ni,Pd)3Sn4 IMC and ENEPIG surface finish after aging at 115°C for 300 h. The overall IMC growth rate of Sn-58Bi solder joint was higher than that of Sn-58Bi epoxy solder joint during aging. The shear strength of Sn-58Bi epoxy solder was about 2.4 times higher than that of Sn-58Bi solder due to the blocking effect of epoxy, and the shear strength decreased with increasing aging time.

Design of Arrays of Linearly Polarized Patch Antennas on an FR4 Substrate: Design of a probe-fed electrically equivalent microstrip radiator

A new strategy for designing probe-fed electrically equivalent microstrip radiators based on their electrical dimensions is discussed in this article. Radiators on a Flame Retardant 4 (FR4) substrate are synthesized for equivalent performance, aiming at lower H-plane cross polarization over the bandwidth and resistive input impedance at the operating frequency. The effect of mutual coupling is analyzed for two classical arrangements: side-by-side and collinear configurations. With the proposed strategy, a broadside collinear array of linearly polarized rectangular patches is designed to operate at the center frequency of the industrial, scientific, and medical (ISM) band (2.45 GHz) on a moderately thick FR4 substrate. The array is designed for low cross polarization in the H-plane and to comply with the specified directivity and side lobe level (SLL). Special attention to the beamforming circuit design leads to a radiation efficiency near 70%.

Compact Dual-Band Suspended Microstrip Slot Antenna with an Antipodal Parasitic Element for WLAN Applications

In this paper, a dual-band microstrip slot antenna over a suspended substrate with an antipodal parasitic element is proposed for wireless local area network systems operating at 2.4, 5.2, and 5.8 GHz. The antenna is composed of multi layers of flame retardant-4 (FR4) and air/foam substrates. The foam/air substrate is included a coaxial single-feed pin and the FR4 substrate is comprised of a modified T-shaped patch and an antipodal modified U-shaped parasitic element with a modified slot around it. The slot antenna configuration improves the compactness, the impedance bandwidth, and the radiation pattern. The realized antenna is proportionately small in size (17 × 20 mm2) and experimental result shows that the antenna covers 2.39---2.5 and 5.1---6.05 GHz with the 10-dB return loss bandwidth. Furthermore, the antenna has good radiation patterns in both x---z and y---z planes over the desired frequency ranges.

A DOUBLE E SHAPED MICROSTRIP PATCH ANTENNA FOR MULTIBAND APPLICATIONS

This paper presents a dual band Compact double E shaped Microstrip Patch antenna with enhanced gain for Worldwide Interoperability for Microwave Access (WI-MAX), Universal Mobile Telecommunication Systems (UMTS) and Satellite applications. The modified E shaped patch antenna is designed using CADFEKO and the results of return loss, Voltage Standing Wave Ratio (VSWR), gain of the proposed antenna are compared with a conventional E shaped patch antenna. The results show that the double E shaped wideband patch antenna has an impedance bandwidth of 10.7 % with a return loss of -13.6dB, -12.4 dB, -12.1dB and -14.2dB at resonant frequencies of 1.96 GHz, 3.62 GHz, 5.76 GHz and 6.82 GHz, whereas a conventional E shaped patch antenna operates at 2.5 GHz, 3.4 GHz and 5.5 GHz with a return loss of -16 dB each and impedance bandwidth of 10.6 %. Both the antennas uses Coaxial Probe feeding technique and Flame Retardant 4 (FR-4) as the substrate material with a thickness of 2.87 mm. A parametric study has been done so as to understand the effect of each parameter to obtain a better performance and optimised results.

Effect of heat treatment temperature and surface roughness to the PDMS-FR4 adhesive bonding

The current work investigates the use of liquid polydimethylsiloxane (PDMS), with a 10:1 ratio of prepolymer:curing agent = 10:1 as the intermediate layer for adhesive bonding with Flame Retardant 4 (FR4). The spin coating of liquid PDMS on FR4 allows irreversible adhesive bonding with the solid PDMS. The strength of the proposed adhesive bonding technique has been investigated under different treatment temperatures: oven-heated at 60 °C, 70 °C, and 80 °C, cooled down in the room temperature of 25 °C, and exposed to direct sunlight at 35 °C. All the samples were left for 6 h. Investigations were conducted to analyze the effect of FR4 surface roughness on the strength and quality of the adhesive bonding. The standard procedure of American Standard Test Measurement (ASTM) D1002 was followed to verify the strength of PDMS-FR4 adhesive bonding. Strongest adhesive bonding, free from air bubbles, was obtained from a sample with smooth surface of FR4 that has undergone a cooling down treatment in the room temperature of 25 °C. FR4 was coated by solder mask to obtain smooth surface. The techniques reported in this paper are simple, straightforward, and effective to be implemented with FR4 as a base material for adhesive bonding with PDMS, thus eliminating expensive and complicated operating equipment as widely used in the oxygen plasma-assisted bonding treatment. Another benefit from this adhesive bonding technique is the fact that it avoids the use of expensive oven or hot plate.

Characterization of Inkjet-Printed Silver Patterns for Application to Printed Circuit Board (PCB)

In this paper, we describe the analysis of inkjet-printed silver (Ag) patterns on epoxycoated substrates according to several reliability evaluation test method guidelines for conventional printed circuit boards (PCB). To prepare patterns for the reliability analysis, various regular test patterns were created by Ag inkjet printing on flame retardant 4 (FR4) and polyimide (PI) substrates coated with epoxy for each test method. We coated the substrates with an epoxy primer layer to control the surface energy during printing of the patterns. The contact angle of the ink to the coated epoxy primer was 69˚, and its surface energy was 18.6 mJ/m². Also, the substrate temperature was set at 70℃. We were able to obtain continuous line patterns by inkjet printing with a droplet spacing of 60 ㎛. The reliability evaluation tests included the dielectric withstanding voltage, adhesive strength, thermal shock, pressure cooker, bending, uniformity of line-width and spacing, and high-frequency transmission loss tests.

Design of Inset Microstrip Patch Antenna for Wireless Power Transmission at 2.45 GHz

In communication systems, there are various types of microstrip antenna that can be used for many applications. This paper mainly focuses on the simple design of an inset rectangular microstrip patch antenna to operate at a frequency of 2.45 GHz for rectenna design. The study involves using an high frequency structure simulator to design the antenna dimensions and to determine its performance. This antenna is based on a thickness of 1.6 mm flame retardant 4 (FR-4) substrate having a dielectric constant of approximately 4.7, an inset feed, and a ground plane. After simulation, the antenna performance characteristics such as its return loss, voltage standing wave ratio, gain, and radiation pattern were obtained and compared with the fabricated measured antenna.

Moisture induced interface weakening in ACF package

One interesting degradation mechanism in flip–chip interconnections using anisotropic conductive film (ACF) is delamination between the adhesive and the sandwiched material. To understand the delamination process, an attempt was made to quantitatively measure the interfacial fracture toughness of both silicon/ACF and flame retardant 4 (FR4)/ACF sandwiched specimens exposed to various humidity conditions using a 4-point bending test. For moisture absorption, specimens were stored inside a humidity chamber (85 °C, 85% RH) until they were fully saturated, and a pressure cooker test (PCT) was additionally performed to expose the specimen to harsher environmental conditions. Delamination occurrence after moisture absorption was checked by means of a scanning acoustic microscope (SAM). Based on the experimental results, we have determined the energy release rate of each interface under different humidity conditions and have located the weaker region where crack initiation would be likely to occur under service conditions in interconnections using ACF. Evidence of crack propagation along the interface was checked by cross section optical images and scanning electron microscopy (SEM). By comparing the results of the specimens under different humidity conditions, interface weakening by moisture absorption was observed and quantitatively analyzed. Interestingly, we found that ACF can show severe degradation of adhesion strength caused by moisture absorption without any delamination occurring.

Advanced imaging with dynamic focus and extended depth using integrated FR4 platform

A two-degrees-of-freedom scanned beam imaging system with large dynamic range and dynamic focusing is demonstrated. The laser diode, photo-detector and the optical components are integrated on a moving platform that is made of FR4 (Flame-Retardant 4), a common polymeric substrate used in printed circuit boards. A scan angle of 52 degrees is demonstrated at 60 Hz resonant frequency while the laser is moved 250 um in the out-of-plane direction to achieve dynamic focusing. The laser is scanned by physically rotating the laser diode and the collection optics to achieve high signal-to-noise ratio and good ambient light rejection. The collection optics is engineered such that the collection efficiency decreases when collecting light from close distances to avoid detector saturation. The detection range is extended from contact distance up to 600 mm while the collected power level varies only by a factor of 30 within this long range. Slight modifications will allow increasing the detection range up to one meter. This is the first demonstration of a laser scan engine with such a high degree of integration of electronics, optoelectronics, optics and micromechanics on the same platform.

FR4 Laser Scanner With Dynamic Focus

An electromagnetically actuated optical scanner made using standard printed circuit board technology with integrated dynamic focusing feature is presented. Dynamic focus is achieved with an independently controlled plunger machined on the flame retardant-4 (FR4) platform. Integration of a laser diode and lens, torsional scanner, and the plunger for dynamic focus adjustment on FR4 platform greatly improves the form factor of the device for imaging applications. A peak-to-peak mechanical scan angle of 50deg is achieved. The dynamic focus control allows for shifting the beam waist location from 80 mm up to 650 mm.